Poly(ethylene
oxide), PEO, based solid polymer electrolyte with
different loadings of a lithium salt, lithium bis(trifluoromethanesulfonyl)imide
(LiTFSI), has been investigated to study the role of PEO–Li
cross-linking on segmental dynamics and free volume structure of PEO
which consequently determine thermal, mechanical, and ion conduction
properties of the electrolyte. In order to investigate the interrelation
between segmental dynamics, free volume structure, and ion conduction
mechanism, broadband dielectric spectroscopy and positron annihilation
spectroscopy have been employed. The ion conduction process in the
polymer electrolyte has been explained according to Almond–West
formalism considering two different universalities dominating at different
temperature or frequency regimes. Ionic conductivity was observed
to increase in a nonlinear trend with salt loading, confirming the
additional role of the ion diffusion process. The present study has
shown that segmental dynamics and free volume structure of PEO-electrolyte
which primarily govern the ion diffusion process are interrelated.
These have been invoked to explain the observed variations in ionic
conductivity, crystallinity, ductility, and thermal stability of PEO–LiTFSI
electrolytes.
Limited ionic conductivity of polymer electrolytes is a major issue in their industrial application. Enhancement in ionic conductivity in Poly (ethylene oxide), PEO, based electrolyte have been achieved by loading...
Crystal
downsizing of zeolitic imidazolate framework-8 (ZIF-8)
has been shown to affect the flexibility of its framework, leading
to the occurrence of “gate-opening”
phenomenon at higher applied gas pressures compared to larger size
crystals. In the present study, we have investigated the crystal size-dependent
pore architecture of crystalline desolvated ZIF-8 samples which is
expected to play the most deterministic role in its gas adsorption
behavior. In order to avoid the pressurization or gas molecule–ZIF
interaction, positron annihilation spectroscopy has been used to investigate
the pores’ sizes, pores’ interconnectivity, and pores’
elemental surface characteristics of desolvated ZIF-8 samples. The
studied ZIF-8 samples (size ∼14 nm −1.4 μm) have
been synthesized at room temperature and systematically characterized
for their phase purity, structural integrity, morphology, and thermal
stability using complementary characterization techniques. Positronium
annihilation from inter-crystal voids as a result of its diffusion
through the crystals indicates that the pore network is highly interconnected
in smaller size crystal samples. However, some interconnections from
deep inside of larger crystals to the outer surface are observed to
be blocked due to the imperfections produced in pore networking during
crystal growth. The present study confirms that crystal downsizing
results in modifications of average pore size corresponding to the
aperture and central cavity. The average aperture size in nanometer
size ZIF-8 crystals (size ∼14 and 45 nm) was measured to be
smaller than the perfect lattice aperture (0.34 nm). We attribute
this smaller aperture size in ZIF-8 nanocrystals to the occurrence
of “gate-opening” phenomenon at higher
applied gas pressure. The surface of nanocrystals is observed to be
enriched by Zn compared to imidazole.
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